#!/usr/bin/perl
$abc="abc";
print "abc=$abc\n";

$src="jeffs";
$src =~ s/\bjeff(?=s\b)/jeff'/g;
# $src =~ s/\bjeffs/jeff's/g;
# $src =~ s/\b(jeff)(s)/$1'$2/g;
# $src =~ s/(?=s\b)(?<=\bjeff)/'/g;
# $src =~ s/(?<=\bjeff)(?=s\b)/'/g;
print "src=$src\n";


$num1="11122233344455567";
# $num1 =~ s/(?<=\d)(?=(\d\d\d)+$)/,/g;
$num1 =~ s/(?<=\d)(?=(?:\d\d\d)+$)/,/g;
print "num1=$num1\n";

$num2="the number is 11122233344455567 haha";
$num2 =~ s/(?<=\d)(?=(\d\d\d)+\b)/,/g;
print "num2=$num2\n";

# \b
$b1 = "abc xyz gogo ha xi";
# right blank && left not blank  +  left blank && right not blank
# $b1 =~ s/(?=\w)(?<!\w)|(?!\w)(?<=\w)/_/g;
$b1 =~ s/\b/_/g;
print "b1=$b1\n";

$ver="1.05.20";
$ver =~ m/(\d+)\.(\d+)\.(\d+)/g;
print "$1, $2, $3\n";